just a bit of info for anyone that gets a similar fault.
we have a wartran that started loosing red from time to time on one of the rptv's.
at first i put it down to a gun fault but after a couple of hours it became obvious it was a signal problem from the pc,anyway it turned out to be a bad vga to dvi adaptor
the other tech advised sending the whole rptv back to the distributor for repair!!!